A method for forming silicon oxide layers on silicon wafers by a wet oxidation process that utilizes a dual-stage pyrolysis is described. The process can be carried out by flowing a first H2/O2 mixture that has a first H2/O2 gas mixture ratio into a torch and then feeding water vapor generated into the wet oxidation chamber to form a first layer of silicon oxide, and then flowing a second H2/O2 mixture that has a second H2/O2 gas mixture ratio into the torch and feeding water vapor generated into the wet oxidation chamber for forming a second thickness of the silicon oxide layer. The second H2/O2 ratio is smaller than the first H2/O2 ratio by at least ⅓ of the value of the first H2/O2 ratio. For instance, when the first H2/O2 ratio used is large than 1.5, the second H2/O2 ratio used is less than 1.2. In one example, the first H2/O2 gas mixture ratio utilized is 1.8, while the second H2/O2 gas mixture ratio utilized is 1.0. It has been found that by reducing the hydrogen content, i.e. by decreasing the H2/O2 gas mixture ratio, the partial pressure of the water vapor generated is reduced which minimizes the loading effect in the furnace tube during the wet oxidation process and improves the uniformity of the silicon oxide layers deposited.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method for forming silicon oxide by wet oxidation comprising the steps of: providing an oxidation chamber equipped with a torch and a conduit providing fluid communication between said chamber and said torch, positioning a plurality of silicon wafers in said oxidation chamber, flowing a first H 2 /O 2 mixture having a first H 2 /O 2 gas mixture ratio into said torch and feeding water vapor generated through said conduit into said oxidation chamber for a first time period, said first time period is between about 30 min. and about 90 min., and flowing a second H 2 /O 2 mixture having a second H 2 /O 2 gas mixture ratio into said torch and feeding water vapor generated through said conduit into said oxidation chamber for a second time period, said second time period is between about 1.0 min. and about 30 min., said second H 2 /O 2 gas mixture ratio being smaller than said first H 2 /O 2 gas mixture ratio by at least of the value of said first H 2 /O 2 gas mixture ratio.
2. A method for forming silicon oxide by wet oxidation accordingly to claim 1 , wherein said second time period being smaller than said first time period.
3. A method for forming silicon oxide by wet oxidation accordingly to claim 1 , wherein said second time period being between about 10% and about 40% of said first time period.
4. A method for forming silicon oxide by wet oxidation accordingly to claim 1 , wherein said first H 2 /O 2 gas mixture ratio being larger than 1.2 and said second H 2 /O 2 gas mixture ratio being smaller than 1.2.
5. A method for forming silicon oxide by wet oxidation accordingly to claim 1 , wherein said first H 2 /O 2 gas mixture ratio being larger than 1.6 and said second H 2 /O 2 gas mixture ratio being smaller than 1.1.
6. A method for forming silicon oxide by wet oxidation accordingly to claim 1 further comprising a nitrogen purging process and an oxygen annealing process.
7. A method for forming silicon oxide by wet oxidation accordingly to claim 1 further comprising a nitrogen purging process for stopping said flow of H 2 /O 2 .
8. A method for growing oxide on silicon wafers by wet oxidation comprising the steps of: providing a wet oxidation chamber equipped with a torch and a conduit providing fluid communication between said chamber and said torch, flowing a first H 2 /O 2 mixture having a H 2 /O 2 gas mixture ratio larger than 1.5 into said torch and feed water vapor generated through said conduit into said wet oxidation chamber for a first time period, and flowing a second H 2 /O 2 mixture having a H 2 /O 2 gas mixture ratio smaller than 1.2 into said torch and feed water vapor generated through said conduit into said wet oxidation chamber for a second time period.
9. A method for growing silicon oxide on silicon wafers by wet oxidation according to claim 8 further comprising of the step of positioning each of said plurality of silicon wafers horizontally in a vertical stack.
10. A method for growing oxide on silicon wafers by wet oxidation according to claim 8 further comprising of the step of flowing H 2 and O 2 individually into said torch for mixing in said torch and reacting pyrolytically to produce H 2 O vapor.
11. A method for growing silicon oxide on silicon wafers by wet oxidation according to claim 8 , wherein said first time period being at least, two times of said second time period.
12. A method for growing silicon oxide on silicon wafers by wet oxidation according to claim 8 , wherein said first time period being at least three times of said second time period.
13. A method for growing silicon oxide on silicon wafers by wet oxidation according to claim 8 , wherein said first time period being more than 40 min. and said second time period being less than 20 min.
14. A method for growing silicon oxide on silicon wafers by wet oxidation according to claim 8 , wherein said second H 2 /O 2 gas mixture ratio being smaller than said first H 2 /O 2 gas mixture ratio by at least of the value of said first H 2 /O 2 gas mixture ratio.
15. A method for growing silicon oxide on silicon wafers by wet oxidation according to claim 8 further comprising the step of depositing silicon oxide layers on said plurality of silicon wafers to a thickness of at least 1000 .
16. A method for growing silicon oxide on silicon wafers by wet oxidation according to claim 8 further comprising the step of depositing silicon oxide layers on said plurality of silicon wafers to a thickness of at least 2000 .
17. A dual-stage wet oxidation process for forming silicon oxide comprising the steps of: providing an oxidation chamber equipped with a torch and a conduit providing fluid communication between said chamber and said torch, positioning a plurality of silicon wafers horizontally in a vertical stack in said chamber, flowing a H 2 /O 2 mixture having a H 2 /O 2 gas mixture ratio larger than 1.5 into said torch and feeding water vapor generated through said oxidation chamber for more than 40 min. in a first stage for forming a first thickness of silicon oxide, and flowing a H 2 /O 2 mixture having a H 2 /O 2 gas mixture ratio smaller than 1.2 into said torch and feeding water vapor generated through said conduit into said oxidation chamber for less than 20 min. in a second stage for forming a second thickness of silicon oxide.
18. A dual stage wet oxidation process for forming silicon oxide according to claim 17 further comprising the step of forming said first and second thicknesses of silicon oxide on said plurality of silicon wafers to a total thickness of at least 2000 .
19. A dual stage wet oxidation process for forming silicon oxide according to claim 17 further comprising a nitrogen purging step and an oxygen annealing step after said first and second stage of forming silicon oxide.
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January 13, 2000
April 16, 2002
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